#include<stdio.h>
//#include<conio.h>
int n,sum;
int main()
{
  //freopen("g.in","r",stdin);
  int i,j,k;
  char s1[50],s2[50],s3[50];
  char c;
  while (scanf("%d",&n)!=EOF)
    {
	  sum=0;
	  scanf("%c",&c);
	  scanf("%s",s1);
	  scanf("%c",&c);
	  scanf("%s",s2);
	  scanf("%c",&c);
	  scanf("%s",s3);
	  for (i=0;i<n;i++)
	    {
		  sum+=2;
		  if (s1[i]==s2[i]) sum-=1;
		  if (s1[i]==s3[i]) sum-=1;
		  if (s2[i]!=s3[i] && s1[i]!=s2[i] && s1[i]!=s3[i]) sum-=1;
		}
	  printf("%d\n",sum);
	}
  //getch();
}
